Such a process is known from e.g. U.S. Pat. No. 5,359,118. This document discloses a process in which di(C1-C4 alkyl) carbonates are prepared by transesterification of an alkylene carbonate with a C1-C4 alkanol. In this process the alkylene carbonate and an alkanol feedstock are reacted countercurrently in a column. The alkylene carbonate is introduced into the upper part of the column and trickles down from above. The alkanol feedstock comprising a pure alkanol and a stream, comprising the alkanol and also the dialkyl carbonate, is fed into the column at a lower part. The alkanol flows upward and reacts countercurrently with the alkylene carbonate to obtain dialkyl carbonate with unreacted alkanol as the top effluent and the alkanediol with any entrained alkanol as the bottom effluent. The top effluent is subjected to extractive distillation to yield an alkanol-rich stream comprising the alkanol and minor amounts of the dialkyl carbonate. This stream is fed to the column as part of the alkanol feedstock.
The process discloses the formation of high-boiling by-products, such as polyglycols. However, the known process does not address the problem of the build up of low-boiling by-products. Such by-products can for instance be carbon dioxide that may be formed due to the hydrolysis of alkylene carbonate by small amounts of water that may be present in the alkanol or any other starting material. Other by-products that may be formed include acetaldehyde, propionaldehyde, and acetone.